Concrete is a construction material formed from a mixture of gravel, pebbles, broken stone or slag and sand in a mortar or cement mix. Concrete is prepared by mixing these dry components with water to form a pourable slurry. The concrete slurry normally is poured or placed into a lumber or metal frame and allowed to dry. The drying rate of unset concrete is often controlled to prevent cracking of the final concrete. Upon drying, the hardened concrete is useful for many surfaces including roads, sidewalks and interior or exterior floors.
Poured concrete, particularly exterior concrete, is subject to permanent staining by paint from nearby work areas, oil drips from vehicles and the like. Concrete is also subject to erosion from exposure to natural elements and is subject to dusting from wear caused by vehicles or feet traveling over the concrete. Concrete is also susceptible to spalling from salt and other road maintenance chemicals. It is known to protect poured concrete from the environment and chemicals by adding various materials to increase its durability and chemical resistance.
One approach for protecting concrete is described in U.S. Pat. No. 4,430,463, where the surface of a substance such as concrete is coated with an acrylic polymer cement coating. The coating composition is a wet mix of Portland cement, acrylic polymer, propylene glycol and a defoamer. A batch of the wet mix is prepared by first preparing three premixes, namely, (1) a premix of the cement and sand, (2) a water dispersion of an acrylic polymer, and (3) an aqueous solution of propylene glycol and a defoaming agent. The three premixes are then combined and mixed with water for three to four minutes. The consistency is varied by adding different amounts of water to obtain a desired consistency. Control of the consistency is important because the composition may be applied to the substrate by a variety of coating methods such as troweling or by spraying onto the substrate which can include set concrete, concrete block, wood panels, hardboards, metal panels, glass panels, and the like. The composition must carefully and evenly be applied to these surfaces. This coating composition requires several preparation steps, uses heavy materials (cement and sand) which are relatively difficult to transport, must be varied according to its application site, and is relatively labor intensive.
Control of the curing rate of freshly poured concrete also provides an opportunity to protect the end product. Methods and compositions used to retard the curing of concrete mixes are well known. Such compositions are generally sprayed onto the finished surface of freshly poured concrete and operate to decrease the evaporation rate of water from the wet mix, thus retarding the drying time of the concrete mix to form a better end product. Problems with retarding the curing rate to affect the final properties of concrete include substantial delays in the ability to use the concrete surface after pouring and costs attendant to such delays. Further, merely delaying curing does not necessarily strengthen the concrete and does not provide the concrete with a protective coating that is long lasting and can protect the concrete from weathering, erosion or chemical attack.
Further, materials for coating concrete must be transported to the job site and often must also be prepared at the job site with complex mixing operations resulting in increased costs, increased delays, and increased efforts. A need remains in the art for a simple method of increasing the durability and flexibility of poured concrete. A further need remains in the art for a concrete coating composition which is relatively easy to transport and can be prepared with minimal labor at the job site.